Method and apparatus for determining electrical contact wear

ABSTRACT

A fluorescent trace material is provided within at least a portion of an electrical contact or interrupter assembly component, or a cavity defined therein. At least a portion of the fluorescent trace material is exposed or released from the electrical contact or interrupter assembly component, indicating a degree of component wear.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation in part of U.S. Ser. No.10/318,859, filed on Dec. 13, 2002, entitled METHOD AND APPARATUS FORDETERMINING ELECTRICAL CONTACT WEAR currently pending [Attorney DocketNo. 24327-P003US], by inventor Bruce Nichols.

FIELD OF INVENTION

[0002] The present invention relates in general to electrical switchingmechanisms (“switches”) and in particular to detecting the extent oferosion or wear of electrical contacts and arc interrupter assembly(“interrupter assembly”) components caused by arcing or other wearprocesses and/or mechanisms, including but not limited to mechanicalwear.

BACKGROUND OF INVENTION

[0003] A variety of electrical equipment contains switches whichinterrupt or direct the path of electricity through an electric circuit.Circuit breakers, for example, are switches used to open a circuit inthe event of a fault, short circuit or similar breaks in current or tointentionally isolate equipment for inspection or maintenance. Anothertype of switch is a load tap changer, which is used to automaticallyselect a particular tap corresponding to a connection within thesecondary windings of a transformer in order to increase or decrease theamount of voltage transformation required as loading conditions change.

[0004] The parts of a switch which actually perform the function ofconnecting and disconnecting the current path are called electricalcontacts (“contacts”). In high voltage equipment, the contacts ofelectrical switches operating under load generally erode over timeduring normal operation. The erosion of electrical contacts mostcommonly results from the arcing that occurs whenever a switch breaks,or interrupts, a circuit. An arc is formed as the electrical contactsmove apart from or toward each other and the electro motive potentialbetween them causes electrons to bridge the inter-contact space regionwith a corresponding electrical discharge. A current is maintained inthe arc until the spacing between the contacts, and thus the impedanceincreases enough to prevent electrons from bridging the gap for thegiven voltage potential, or, if moving toward each other, until thecontacts are touching. As well, current flowing across the gap generatesextreme heat, resulting in temperatures high enough to burn away some ofthe contact material.

[0005] Erosion of the contacts can cause respective mechanism failuresor deteriorated switch operation, and otherwise generally reduce orlimit the useful lives of the switches themselves. Switches may failwhen their contacts have eroded to such a degree that they cannoteffectively complete a circuit, or when the erosion has changed thephysical shape of the contact such that the mechanical operation of theswitch is interrupted. Once a contact has eroded to the point at whichfurther use risks injury to personnel or machinery, known as the“critical point,” a contact's useful life is over.

[0006] Because arcing and erosion cannot be eliminated, standardindustry practice is such that switches are almost always designed toallow replacement of the contacts. It is typically less expensive toreplace worn contacts than to replace an entire switch when the contactshave eroded to the critical point or close thereto. As a result, usersof switches must monitor the erosion of the contacts to recognize whenthe predetermined critical point is approaching or has been reached.Replacing worn contacts at or before the critical point is importantbecause contacts used past that point continue to erode and may causethe switch to fail. A switch failure can have a negative or catastrophiceffect on equipment and presents a danger to personnel. Further, such aswitch failure can reduce the confidence of integrity and stability of arespective regional grid, which can have a material financial and othersuch effects on residential, commercial, and institutional users of thatgrid. On the other hand, replacing contacts before the end of theiruseful life increases material and labor costs.

[0007] There is a large expense associated with electrically isolating,or de-energizing, and physically inspecting high voltage electricalequipment to determine the extent of wear or erosion of the contacts.This expense is compounded by the necessity of removing, storing, andprocessing a large quantity of oil, sometimes up to 1000 gallons.Contacts are often replaced early due to the difficulty of predictingthe rate of erosion from one maintenance cycle to the next. The expenseof inspecting the contacts is often so great that typically maintenancedepartments change some of the contacts during every inspection, eventhough the contacts may have months or more of useful life remaining.Properly matching the timing of inspection with the end of the usefullife of the contacts would thus advantageously result in a cost savings,and likely reduce the overall cost of ownership for a utility's grid.

[0008] One means or process or method commonly used to monitorelectrical equipment performance, and identify equipment requiringmaintenance, is to perform or conduct a Dissolved Gas Analysis (DGA).The DGA process involves extracting a sample of the oil surrounding thecontacts and, by using gas chromatography, analyzing the oil for thepresence and amount of certain gases dissolved within this insulatingoil. The presence of certain gases is indicative of various types ofevents that may be occurring within the equipment. For example, a highlevel of methane or ethane dissolved in the oil would be indicative ofexcessive heating within load tap changers and transformers whereas theamount of acetylene would have a corresponding relationship with theamount of arcing that is occurring. The DGA method of monitoring,however, lacks the precision necessary to determine the proper timing ofcontact replacement, as the presence of dissolved gases related toerosion has no correlation to the amount or extent of erosion of thecontacts.

[0009] There is accordingly a need to provide a method and apparatus forthe detection of the extent of electrical contact erosion, or wearing,that is inexpensive and may be used by personnel on-site as well as inthe laboratory.

SUMMARY OF INVENTION

[0010] The invention relates to an improved sacrificial electricalcontact or interrupter assembly component. At least a portion of theelectrical contact or interrupter assembly component, or a cavitydefined therein, comprises a fluorescent trace material. At least aportion of the fluorescent trace material is exposed or released,indicating a degree of component wear.

[0011] In one aspect of the invention, a method and apparatus areprovided for detecting the exposed or released trace material.

[0012] In yet another aspect of the invention, a trace material isprovided within certain components of the electrical switching mechanismand, upon wear, may be released or exposed into the surrounding mediumand monitored to detect or indicate component wear.

BRIEF DESCRIPTION OF DRAWINGS

[0013] For a more complete understanding of the present invention, andthe advantages thereof, reference is now made to the followingdescriptions taken in conjunction with the accompanying drawings, inwhich:

[0014] For a more complete understanding of the present invention andthe advantages thereof, reference is now made to the followingdescription taken in conjunction with the accompanying drawings, inwhich:

[0015]FIG. 1 is a perspective view of an interrupter assembly that maybe used within a typical circuit breaker;

[0016]FIG. 2 is a section, taken along line 2-2 of FIG. 1, illustratingthe position and arrangement of typical contact assemblies within theinterrupter assembly;

[0017]FIG. 3a is a partial section of a contact assembly containing acavity and trace material;

[0018]FIG. 3b is a partial section of a contact assembly that hassuffered erosion due to arcing;

[0019]FIG. 4a is a top view of a baffle plate;

[0020]FIG. 4b is a side view of a baffle plate, taken along line 4 b-4 bof FIG. 4a;

[0021]FIG. 5 is a perspective view of a contact assembly containing acavity and trace material;

[0022]FIG. 6 is a partial section view, taken along line 6-6 of FIG. 5,showing the construction and assembly of the contact, cavity and tracematerial in greater detail;

[0023]FIG. 7 is a side view of a transfer switch sacrificial contactassembly containing a cavity and trace material;

[0024]FIG. 8 is a schematic diagram of a fluorescent trace materialmonitoring or detecting system;

[0025]FIG. 9 is a perspective view of a particulate concentration orcollection device employed in connection with monitoring for ordetecting trace material;

[0026]FIG. 10 is a side view, in partial section, of a drain assembly ofa tank or switch compartment including an optically-transmissive conduitand port employed to monitor or detect trace material;

[0027]FIG. 11a is a perspective view of a remote optical access portwithin an equipment control cabinet;

[0028]FIG. 11b is a top view, in partial section, of the remote opticalaccess port of FIG. 11a, taken along line 11 b-11 b of FIG. 11a;

[0029]FIG. 11c is a top view, in partial section, of the remote opticalaccess port of FIG. 11b, with a detached mobile transmission cable;

[0030]FIG. 12 is an emission spectra of oil samples performed duringtesting of one preferred embodiment of the present invention;

[0031]FIG. 13 is an emission spectra of oil samples at emission minimaperformed during testing of one preferred embodiment of the presentinvention;

[0032]FIG. 14 is an emission spectra of Opacity 6 oil with variousconcentrations of a trace material performed during testing of onepreferred embodiment of the present invention;

[0033]FIG. 15 is an emission spectra of dilute oil samples performedduring testing of one preferred embodiment of the present invention; and

[0034]FIG. 16 is the strength emission of a trace material showing theconcentration versus emission detectability performed during testing ofone preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Although the invention has been described with reference tospecific embodiments, these descriptions are not meant to be construedin a limiting sense. Various modifications of the disclosed embodiments,as well as alternative embodiments of the invention will become apparentto persons skilled in the art upon reference to the description of theinvention. It should be appreciated by those skilled in the art that theconception and the specific embodiment disclosed may be readily utilizedas a basis for modifying or designing other structures for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

[0036] It is therefore contemplated that the claims will cover any suchmodifications or embodiments that fall within the true scope of theinvention.

[0037]FIG. 1 shows an interrupter assembly 100 that may be used as partof a circuit breaker (not shown), for example. Interrupter assembliesgenerally are well-known in the art. The interrupter assembly 100includes an interrupter shell 10 surrounding a male contact assembly 12and a female contact assembly (not visible in FIG. 1). The interruptershell 10 is preferably fabricated from a strong, non-conducting materialsuch as phenolic cellulose tubing or fiberglass. The shell 10 wall is ofsufficient thickness to contain the arc and to withstand the forcescreated by the arc-gas expansion during arcing. The interrupter assembly10 is generally housed in an enclosure such as a tank or switchcompartment, and surrounded by an insulating, non-conductive medium suchas oil, air, or an inert gas. In one preferred embodiment of the presentinvention the non-conductive medium is a high dielectric insulating oil.Also shown in FIG. 1 is an exhaust port 14 and an assembly of baffleplates 16.

[0038] In FIG. 2, a female contact assembly 18 is shown within theinterrupter shell 10. The female contact assembly 18 comprises aplurality of contact segments 20, which are preferably arranged in acircular pattern. The contact segments 20 are preferably configured toengage the male contact assembly 12 and are preferably biased toward themale contact assembly 12 to promote electrical contact therewith.

[0039] The baffle plates 16 can be seen more clearly in FIG. 2. Four (4)baffle plates 16 are shown in this embodiment, although a greater orsmaller number may be used and are described in more detail below, inconnection with FIGS. 4a and 4 b.

[0040] Under normal conditions, in one embodiment, the end of thecontact assembly 12 extends into the interrupter assembly 100 via theopening 24 at the base of the interrupter assembly shell 10. Duringoperation, the contact assembly 12 extends through the baffles 16, andpenetrates into, or engages, the female contact assembly 18, allowingelectric current to flow through the assembly. The contacts within theinterrupter assembly are designed to open upon the occurrence of certainevents, such as a fault, or short circuit, or a manual switch (notshown) being tripped. When the circuit breaker is tripped, the contactassembly 12 is rapidly retracted away from the female contact assembly18 and from the interrupter shell 10. As the contact assembly 12 ispulled away from the female contact assembly 18, an arc will typicallyoccur between the contacts.

[0041]FIGS. 3a and 3 b show the contact assembly 12 of one embodiment inmore detail. The contact assembly 12 may comprise a base 32 and acontact tip 34. The base 32 may be constructed from copper, although anyelectrically conductive material may be used. The contact tip 34 may beconstructed from a material resistant to erosion from arcing, such as atungsten-based alloy. The contact assembly 12 may comprise one or morecavities 36, such as defined in the contact tip 34, but mayalternatively be located elsewhere in the contact assembly 12, providedat least a portion of the cavity 36 is subject to exposure to thesurrounding medium (not shown) as a result of erosion due to arcing. Atrace material (not shown) is provided in the cavity 36. The tracematerial (not shown) may be injected into the cavity or the contact tip34 may be brazed onto the base 32 so that a cavity 36 is created withinwhich the trace material is contained.

[0042] As the interrupter assembly 100 is used, the contact tip 34erodes due to arcing. When the contact tip 34 has eroded to the extentthat it breaches the cavity 36, an opening 42 to the cavity is created,as shown in FIG. 3b. The trace material is then in contact with thesurrounding medium, and at least a portion of the trace material isreleased from the cavity 36 into the surrounding medium. The surroundingmedium is monitored for the presence of the trace material, the presenceof which indicates that the contact assembly 12 requires replacement.

[0043] In another embodiment, the fluorescent trace material may,instead, be distributed within the material comprising the contactassembly 12, the contact tip 34, the base 32, or any portion of thesecomponents. In that case, the fluorescent trace material is releasedinto the surrounding medium more gradually as the contact assembly 12,or applicable portion thereof, erodes. At least one point in thesurrounding medium is then monitored until a sufficient quantity oftrace material is detected to indicate that the contact assembly 12should be replaced.

[0044] In one embodiment the trace material preferably comprises atleast one fluorescent trace material. Fluorescent trace material refersto luminescence in which light of a visible color is emitted from asubstance under stimulation or excitation by light or other forms ofelectromagnetic radiation or by certain other means. The fluorescentcomponent emits electromagnetic radiation when it is “excited,” that is,when it is exposed to incident electromagnetic radiation within aparticular frequency range. The molecules comprising the fluorescentcomponent absorb the incident electromagnetic radiation and then emitelectromagnetic radiation, preferably of a different wave-length thanthat absorbed. Preferably, a fluorescent component is chosen with anexcitation wave-length in the ultraviolet range and which emits light inthe visible spectrum upon excitation. Choosing a fluorescent componentwith excitation and emission frequencies within these ranges makesdetection simpler, because the electromagnetic radiation emitted by thefluorescent component may be readily distinguished from reflectedelectromagnetic radiation used for exciting the fluorescent component.

[0045] In one embodiment the fluorescent components comprising the tracematerial may be able to withstand the high temperatures involved in thebrazing process, typically between 1000 and 1250 degrees Fahrenheit.

[0046] The fluorescent trace materials fluoresce when exposed, orexcited, to incident electromagnetic radiation with a broad-band UVlight source and emit in a range diverse to the incident backgroundradiation of the insulating oil. Other fluorescent materials known toone of ordinary skill in the art may also be used as a trace material.

[0047] Semiconductor nanocrystal quantum dots (“nanocrystals,” “quantumdots” or “nanocrystals quantum dots”) are tiny crystals composed ofperiodic groups of II-VI, III-V, or IV-VI materials that range in sizefrom 2-10 nanometers or roughly the size of 10 to 50 atoms in diameter.Due to the extremely small size of the nano-crystals, the optical,electronic, and chemical properties of the quantum dots are dominated byphysical size and the chemistry of their surface. The diameters of thesemiconductor nanocrystal quantum dots are, in fact, smaller than theBohr radius of an electron-hole pair (exciton) formed through a photoninteraction with the nanocrystal resulting in the quantum confinementeffects. The results of quantum confinement are that the electron andhole energy states within the nanocrystals are discrete (similar to a3-d spherical quantum well) where the electron and hole energy levelsare a function of the quantum dot diameter as well as composition. Thelarger the nanocrystals become the smaller the difference between energystates. Because all optical and electronic properties are dependent uponthe energy and density of electron states, the properties can be alteredby engineering size and surfaces of these tiny structures. In effect,quantum confinement results in a controlled blue shifting of the bulkenergy bandgap so that properties such as absorption onset and peakphotoluminescence wavelength are size dependent. In a semiconductornanocrystal quantum dot, strong absorption occurs at specific photonenergies, at the expense of reduced absorption at other energies. Inaddition, quantum confinement effectively enhances many nonlineareffects due to a concentration of the oscillator strength into narrowwavelength bands. These properties include the non-linear refractiveindex (optical Kerr effect), non-linear absorption, quantum confinedStark effect, and other electro- and magneto-optic effects.

[0048] The following is a list of unique linear optical effectsexhibited by semiconductor nanocrystal quantum dots:

[0049] Absorption Spectra of Quantum Dots

[0050] The absorption spectrum appears as a series of overlapping peaksthat get larger at shorter wavelengths. Each peak corresponds to anenergy transition between discrete electron-hole energy levels (exciton)within the nanocrystal. The nanocrystal will not absorb light that has awavelength longer than that of the first exciton peak, also referred toas the absorption onset. At the short wavelength limit the absorption ofthe nanocrystals mimics that of a bulk semiconductor. Like all otheroptical and electronic properties, the wavelength of the first excitonpeak (and all subsequent peaks) is a function of the composition andsize of the nanocrystal. A smaller nanocrystal results in a firstexciton peak at shorter wavelengths.

[0051] Photoluminescence Spectra of Quantum Dots

[0052] The wavelength at which the nanocrystals luminesce is directlyrelated to the nanocrystal size and composition and hence the energydifferences between electron states. By synthesizing a quantum dot of agiven composition to a desired size, the emission wavelength can bechosen. The smaller the difference between the states, the “redder” theemission, thus small nanocrystals will emit “bluer” light and largernanocrystals will emit “redder” light. There is a limit on how “red” or“blue” the luminescence can be tuned. As the nanocrystals grow in sizethey begin to appear more like a bulk semiconductor. Thus the “red”limit is ultimately constrained by the bulk bandgap energy. On the otherhand there is a limit on how controllably small nanocrystals can begrown which results in a practical “blue” limit.

[0053] Quantum Dot Fluorescence I

[0054] The fluorescence wavelength can be tuned from the mid-infraredthrough the visible and into to the ultraviolet wavelength regime,depending on the size and composition of the material. Examples ofquantum dot emissions include Cadmium Selenide from 450 nm to 650 nm andLead Selenide from 900 nm-2000 nm. CdS (from 350 nm to 470 nm), CdTe(from 600 nm to 725 nm), and PbS (from 800 nm to 1600 nm).

[0055] Quantum Dot Fluorescence II

[0056] The peak photoluminescence wavelength is bell-shaped and occursat a slightly longer wavelength than the lowest energy exciton peak (theabsorption onset). An interesting property of semiconductor nanocrystalquantum dots is that the PL wavelength is independent of the wavelengthof the excitation light, assuming that it is shorter that the wavelengthof the absorption onset. The bandwidth of the photoluminescence spectra,denoted as the Full Width at Half Maximum (FWHM) is a function of theintrinsic linewidth of the nanocrystals and the size distribution of thepopulation of nanocrystals within a solution or matrix material.Emission spectra broadening due to size distribution are known asinhomogeneous broadening and are the largest contributor to the FWHM.Narrower size distributions yield smaller FWHM. For CdSe a 5% sizedistribution corresponds to a 30 nm FWHM while in PbSe a 5% sizedistribution corresponds to a 100 nm FWHM.

[0057] Quantum Yield of Quantum Dots

[0058] The percentage of absorbed photons divided that result in anemitted photon is called Quantum Yield (QY). The QY is a function of therelative influences of radiative recombination (producing light) andnonradiative recombination mechanisms (which produce no light).Nonradiative recombination, which is much faster than radiativerecombination, largely occurs at the nanocrystal surface and istherefore greatly influenced by the surface chemistry. It is known thatcapping the nanocrystal with a shell of an inorganic wide bandsemiconductor reduces nonradiative recombination and results in brighteremission. It has also been demonstrated that different surfacechemistries greatly affect QY. For example thiols present on thenanocrystal surface are hole traps and reduce QY while amines are notresulting in brighter nanocrystals.

[0059] Molecular Coupling of Quantum Dots

[0060] Colloidally prepared nanocrystal quantum dots are free floatingand can be coupled to a variety of molecules via metal coordinatingfunctional groups. These groups include but are not limited to thiol,amine, nitrile, phosphine, phosphine oxide, phosphonic acid, carboxylicacid or others ligands. This ability greatly increases the flexibilityand application in which quantum dots can be used. By using the correctmolecules on the surface, the quantum dots can suspend in nearly anysolvent, or be implemented in a variety of inorganic and organic films.In addition the surface chemistry can be used to effectively alter theproperties of the nanocrystal including brightness, and electroniclifetime.

[0061] In one preferred embodiment, the trace material comprises certainsemiconductor nanocrystals quantum dots.

[0062]FIGS. 4a and 4 b illustrate one configuration of a baffle plate 16that may be used in an interrupter assembly 100. The baffle plate 16controls the flow of gases produced as a result of arcing(“arc-gases”)(not shown) through the arc-gas exhaust port 14 and aids inconstricting the arc (not shown) and directing the arc into the exhaustport 14. The arc and arc gases are directed through a reduced sectionchannel 44 defined in the baffle plate 16, which is directed toward theexhaust port 14. The exhaust port 14 is directed toward an arc barrierchamber, which prevents the arc and arc-gasses from contacting the tank,or switch compartment, or other nearby components within the equipment.There is preferably either a notch 48 or a hole (not shown) defined ineach baffle plate 16, which allows the contact assembly 12 to extendthrough the baffle plates 16.

[0063] The baffle plates 16 may be constructed from a non-conductivematerial with sufficient strength to withstand the high forces createdby arcing. Additionally, the baffle plates 16 may be preferablyconstructed from a material that will at least partially vaporize whenexposed to arcing so that any material which is released from the baffleplates 16, as a result of arcing, will be vaporized, rather than remainas particulate debris within the surrounding medium. The baffle plates16 may be constructed from homogeneous cellulose or reinforced melamineresin. Other materials known to one of ordinary skill in the art may beused to construct the baffle plates 16.

[0064] Because of the tendency of baffle plates 16 used in aninterrupter assembly 100 to experience wear over time as a result ofarcing, it is necessary to replace the baffle plates 16 before theybecome so worn that the baffle plates 16 no longer function effectively.In order to determine the optimal replacement time without necessitatingdisassembling the interrupter assembly 100 for visual inspection, onemay use a trace material in the baffle plates 16, similar to the usedescribed above in connection with the contact assembly 12.

[0065] As shown in FIG. 4a, a cavity 46 is defined in the baffle plate16, preferably near the channel 44 and the exhaust port 14. The cavity46 may be created by machining a shallow depression in the underside ofthe baffle plate 16. Another method would be to create a cavity bydrilling a cylindrical hole from a point remote to the area that wouldbe subject to arcing. A trace material (not shown) is provided in thecavity 46. The trace material is preferably a fluorescent trace materialas described herein, although other trace materials may alternatively beused. A cover 47 or plug is preferably provided to seal the cavity 46.The cover 47 or plug preferably is comprised of the same material asthat used for construction of the baffle plates 16. As the baffle plates16 experience wear as a result of arcing, eventually an opening (notshown) to the cavity 46 will develop, allowing at least a portion of thetrace material to escape into the surrounding medium. The surroundingmedium is monitored for the trace material, the presence of whichindicates at least one baffle plate 16 is in need of replacement.

[0066] Alternatively to providing the trace material in one or morecavities, the material may, instead, be distributed within the materialcomprising the baffle plate 16, or any portion of thereof. In such case,the trace material is released into the surrounding medium gradually asthe baffle plate 16, or applicable portion thereof, erodes. At least onepoint in the surrounding medium is then monitored until a sufficientquantity of trace material is detected to indicate that at least onebaffle plate requires replacement.

[0067] The trace material may comprise the same material used as a tracematerial in connection with the contact assembly 12. Alternatively, adifferent trace material may be selected so that, by identifying whichtrace material is present in the surround medium, the user may identifywhether the contact assembly 12 or baffle plates 16 require replacement.Further, a non-fluorescent trace material may be used, provided anappropriate detection means is also used.

[0068] Shown in FIG. 5 is another embodiment of a contact assembly 50including a cavity and trace material. Contact assembly 50 is of thetype that may be used in a load tap changer selector switch that doesnot transfer or divert current during tap changing operations andtherefore experiences arcing during the normal operation of atransformer (not shown). In a selector switch, one or more stationarycontact assemblies 50 are provided for each of the taps of a secondarywinding (not shown) in a transformer. A second part of the selectorswitch, the moving contact assembly (not shown), is used to conductivelyengage the contact assembly 50, thereby allowing selection of thesecondary winding tap chosen by the user. The selector switch, of whichthe contact assembly 50 is a part, switches between taps while underload, causing arcing and erosion.

[0069] The contact assembly 50 includes a base 52 preferably made ofcopper, although any electrically conductive material may be used. Thebase 52 may be provided with one or more holes 54 for mounting to aselector switch. One or more contact tips 56 are bonded to and inelectrical communication with base 54. The contact tips 56 arepreferably made from a material that is conductive and resistant toerosion from arcing, such as a tungsten-based alloy. The contact tips 56are preferably bonded to the base 52 by brazing. In another embodiment,the contact is fabricated entirely from tungsten-based alloy therebyrequiring no brazing.

[0070] The contact tips 56 are provided with one or more cavities 58.Cavities 58 are formed in the contact tips 56 by machining prior toassembly by brazing or by drilling a cylindrical hole from a pointremote to the area that would be subject to arcing such that thecavities 58 are sealed when the contact tips 56 are bonded to the base52. After a cavity 58 is provided, a trace material (not shown) isinserted into the cavity 58, and the contact tip 56 is bonded to thebase 52. The trace material is preferably as described above inconnection with FIGS. 3a and 3 b. In another embodiment, the tracematerial is inserted into the cavity prior to brazing.

[0071] Referring to FIG. 6, a contact tip 56 is shown as a partialsection view along line 6-6 of FIG. 5. A partial representation of thebase 52 is also shown. The contact tip 56 has a front edge 62, which ispreferably beveled. Front edge 62 is the first part of the contact tip56 to touch the second part of the selector switch when the switchcloses, and it is the last part of contact tip 56 to separate from theopposite contact when the switch opens. Therefore, the front edge 62 isthe surface of the contact tip 56 which is most subject to erosion fromarcing.

[0072] As the contact assembly 50 is used, the contact tips 56 erodefrom arcing. When the contact tips 56 have eroded to a sufficientdegree, the cavities 58 are opened. As a cavity 58 is opened, the tracematerial comes into contact with and is dispersed into the surroundingmedium. When the presence of the trace material is detected in thesurrounding medium, replacement of the contact assembly 50 is required.

[0073] Alternatively to providing the fluorescent trace material in oneor more cavities, the material may, instead, be distributed within thematerial comprising the contact assembly 50, the contact tip 56, thebase 52, or any portion of these components. In such case, thefluorescent trace material is released into the surrounding medium moregradually as the contact assembly 50, or applicable portion thereof,erodes. At least one point in the surrounding medium is then monitoreduntil a sufficient quantity of trace material is detected to indicatethat the contact assembly 50 should be replaced.

[0074] Turning now to FIG. 7, another embodiment of a sacrificialcontact is shown. Contact assembly 70 is used in a high voltage load tapchanger to transfer, or divert, the electrical current prior to movementof the selector switch, and is accordingly subject to accelerated arcingand erosion as it operates during each operation of the selector switch.Contact assembly 70 comprises a base 72 and a contact tip 74.Alternatively, the contact may be fabricated entirely from atungsten-based alloy. The contact tip 74 is provided with one or morecavities 76. A fluorescent trace material (not shown) is inserted intothe cavities 76 prior to brazing and/or the cavities created bymachining prior to it being sealed when the contact tip 74 is brazed tothe base 72 or by drilling a cylindrical hole from a point remote to thearea that would be subject to arcing and a fluorescent trace material(not shown) is implanted into the cavities 76; or by any of the variousother methods well known to those of ordinary skill in the art. Thetrace material is preferably as described above in connection with FIGS.3a and 3 b.

[0075] As the contact assembly 70 is used to create and break electricalcircuits, erosion occurs. When the contact tip 74 is eroded to asufficient degree, the cavities 76 are opened. As the cavities 76 areopened, the trace material comes into contact with and is dispersed intothe surrounding medium. When the presence of the trace material isdetected in the surrounding medium, replacement of the contact assembly70 is indicated.

[0076] Alternatively to providing the fluorescent trace material in oneor more cavities, the material may, instead, be distributed within thematerial comprising the contact assembly 70, the contact tip 74, thebase 72, or any portion of these components. In that case, thefluorescent trace material is released into the surrounding medium moregradually as the contact assembly 70, or applicable portion thereof,erodes. At least one point in the surrounding medium is then monitoreduntil a sufficient quantity of trace material is detected to indicatethat the contact assembly 70 should be replaced.

[0077]FIG. 8 is a schematic representation of a means for detecting afluorescent material in a medium surrounding a contact assembly(“surrounding medium”). The detection means comprises an electromagneticradiation source 82. The electromagnetic radiation source 82 generateselectromagnetic radiation that is directed into the surrounding mediumand used to excite any fluorescent trace material present in thesurrounding medium. The electromagnetic radiation source 82 preferablygenerates electromagnetic radiation of a wave-length that is known tocause fluorescence in the particular fluorescent trace material beingdetected. As described above, such wave-length is preferably in thevisible ultraviolet light range; however electromagnetic radiation ofother frequencies may also be used.

[0078] Alternatively, a sample of the surrounding medium may beextracted as a sample and monitored for the presence of the tracematerial using an electromagnetic radiation source either in alaboratory or by a portable instrument used by on-site personnel.

[0079] Alternatively, the material may be monitored via an in-situsensor embodied within or unique to the matrix of the fluorescentmaterial, that transmits status to a receiving device to help assuremonitoring.

[0080] Many sources of ultraviolet light are known and may be used asthe electromagnetic radiation source 82. Examples include fluorescentlamps, incandescent lamps and xenon lamps. The electromagnetic radiationfrom the electromagnetic radiation source 82 is directed into thesurrounding medium using an electromagnetic radiation transmission means84. The electromagnetic radiation transmission means 84 preferablycomprises an optically-transmissive conduit, such as a fiber opticcable. Alternatively, the electromagnetic radiation transmission means84 may comprise a transparent or translucent window or lens (not shown).In another embodiment, the electromagnetic radiation source 82 may beinstalled in the equipment tank (not shown) or switch tank orcompartment (not shown) within which the contact assembly is located sothat a separate electromagnetic radiation transmission means 84 isunnecessary. In yet another embodiment, a sample of the surroundingmedium is removed from the contact assembly housing and analyzed usingan electromagnetic radiation source 82 by maintenance personnel or in alaboratory environment. Alternatively, an in-situ sensor within thefluorescent material itself may be used to transmit status to areceiving device.

[0081] Any fluorescent material present in the surrounding medium willemit its own electromagnetic radiation (“fluorescent radiation”) inresponse to the electromagnetic radiation directed into the surroundingmedium. Fluorescent radiation refers to electromagnetic radiation of anyfrequency that is produced in response to absorption of electromagneticradiation, including by fluorescence, phosphorescence, or otherwave-length specific processes.

[0082] The fluorescent radiation is directed via a fluorescent radiationtransmission means 86 to a fluorescent radiation detection means 88. Thefluorescent radiation transmission means 86 preferably comprises anoptically-transmissive conduit, such as a fiber optic cable.Alternatively, the fluorescent radiation transmission means 86 maycomprise a transparent or translucent window or lens (not shown). Thefluorescent radiation transmission means 86 may comprise the samestructure or a different structure as the fluorescent radiationtransmission means 86. Most preferably, the fluorescent radiationtransmission means 86 and the electromagnetic radiation transmissionmeans 84 comprise a single optical fiber. Alternatively, the fluorescentradiation detection means 88 may be installed within the tank or switchcompartment within which the contact assembly is located so that afluorescent radiation transmission means 86 is unnecessary.Alternatively, a piezo-electric circuit that converts, amplifies andmodulates the fluorescent radiation transmission may be used.Additionally, a sample of the surrounding medium may be removed from thecontact assembly tank or switch compartment and analyzed usingfluorescent radiation detection means 88 by on-site personnel or in alaboratory environment.

[0083] The fluorescent radiation detection means 88 may comprise anymeans that is useful for converting the fluorescent radiation into formusable for detection. Preferably, the fluorescent radiation detectionmeans 88 comprises a photodiode (not shown) which converts theelectromagnetic radiation into an electrical signal. Alternatively, thefluorescent radiation detection means 88 may comprise an amplifier (notshown) which increases the intensity of the fluorescent radiation to alevel that may be visually detected. In another embodiment, sufficientfluorescent material may be used that the concentration of fluorescentmaterial in the surrounding medium is high enough to produce visiblelight without amplification.

[0084] If the fluorescent radiation detection means 88 comprises aphotodiode or similar device which converts the fluorescent radiationinto an electrical signal, then the electrical signal thus created istransmitted to a display means 92. The display means may be as simple asan LED which emits light when a current is applied. Alternatively, thedisplay means 92 may comprise an analog meter. In another alternative,the display means 92 may comprise a processor which converts the signalto a digital quantity able to be displayed on an LCD display, forexample. In yet another embodiment, especially where the electromagneticradiation source 82 and fluorescent radiation detection means 88 areinstalled on the exterior of the equipment tank or switch compartment,the display means 92 comprises a transmitter which transmits thedetected information by low voltage electrical connection, radiofrequency or other methods to a remote observation site (not shown).Alternatively, the concentration of material may be transmitted suchthat there is a color display or some other indicator level havingcorresponding significance to the monitoring personnel. Additionally, itis noted that in certain embodiments a display means is not necessary.

[0085] Shown in FIG. 9 is a particulate concentration device 94 that maybe used to aid in the detection of fluorescent trace material in thesurrounding medium. The particulate concentration device 94 isconfigured for use in equipment having a forced-circulation system forfiltering the oil surrounding the contacts. The particulateconcentration device 94 is preferably located on a conduit which directsthe flow of oil through the circulation system. A filter bed 106,constructed from a filtering material, substantially covers the area ofoil flow through the particulate concentration device 94. The filter bedis preferably tapered in the direction of oil flow and preferablyterminates at a collection surface 108.

[0086] As oil circulates through the particulate concentration device94, some of the fluorescence trace material present in the oil, if any,will collect on the collection surface 108. In this embodiment, anoptical transmission conduit 107 serves as the electromagnetic radiationtransmission means 84 and the fluorescent radiation transmission means86. The optical transmission conduit 107 extends through a wall of theparticulate concentration device 94 to a position near the collectionsurface 108. A fitting 109 is provided in the wall of the particulateconcentration device 94 to provide a seal around the opticaltransmission conduit 107. An end of the optical transmission conduit 107is held in place by a first brace 111. Alternatively, a particulateconcentration device 94 may be utilized with any trace material, notonly a fluorescent trace material.

[0087] Electromagnetic radiation from the electromagnetic radiationsource 82 is directed to the collection surface 108. Some of thefluorescent radiation produced by the fluorescent trace material on thecollection surface 108 is directed through the fluorescent radiationtransmission means 86 to a fluorescent radiation detection means 88.

[0088] Shown in FIG. 10 is a particulate collection reservoir 116, whichmay be used in a tank or switch compartment as an alternative to theparticulate concentration device 94 of FIG. 9, especially in a tank orswitch compartment which does not include a forced-circulationfiltration system. The particulate collection reservoir 116 ispreferably located on a floor 117 of the tank or switch compartment, ata point at which fluorescent trace material is likely to settle afterbeing released from a cavity in a contact assembly or baffle plate, forexample. A particulate collection funnel 119 is preferably positionedover the particulate collection reservoir 116 to aid in the collectionof the trace material; however, the particulate collection funnel 119may alternatively be omitted.

[0089] Again in this embodiment, an optical transmission conduit 115serves as an electromagnetic radiation transmission means 84 and afluorescent radiation transmission means 86. The optical transmissionconduit enters the tank or switch compartment through a port 112,provided in a portion of a drain pipe 113, having an access opening 114.The access opening 114 is preferably nearer to the tank or switchcompartment than a drain valve 120.

[0090] The end of the optical transmission conduit 115 is preferablypositioned so that electromagnetic radiation from the electromagneticradiation source 82 is directed towards a translucent or transparentobservation wall 118 of the particulate collection reservoir 116. Anyfluorescent trace material within the particulate collection reservoir116 is excited by the electromagnetic radiation. A portion of theresulting fluorescent radiation, if any, is transmitted through thefluorescent radiation transmission means 86 to a fluorescent radiationdetection means 88.

[0091]FIGS. 11a, 11 b and 11 c illustrate a remote access port 122through which an electromagnetic radiation source 82 and fluorescentradiation detection means 88 may access the oil or other mediumsurrounding a switch. Preferably, one end of a permanent transmissioncable 124 is connected to the remote access port 122, while an oppositeend (not shown) is positioned at an appropriate place in the tank orswitch compartment. The remote access port may be used in conjunctionwith the embodiments shown in either FIG. 9 or 10, or other embodiments.

[0092] The remote access port 122 is preferably mounted on a wall 127 ofan equipment control cabinet 123, to allow for easy access by anoperator. In FIG. 11a a generic instrument panel 132 is shown in brokenlines to aid in interpretation of the drawing. The remote access port122 is preferably held in place by a second brace 126. Alternatively,the remote access port 122 may be mounted to an existing instrumentpanel, such as generic instrument panel 132, for example. When not inuse, the remote access port 122 is preferably enclosed behind a door 130to the equipment control cabinet.

[0093] The remote access port 122 is configured to engage an end of amobile transmission cable 128 and to allow transmission ofelectromagnetic radiation from the mobile transmission cable 128 to thepermanent transmission cable 124 and vice versa. The end of the mobiletransmission cable 128 is preferably configured for easy installationinto and removal from the remote access port 122. In this embodiment,the mobile transmission cable 128 and permanent transmission cable 124serve as an electromagnetic radiation transmission means 84 and afluorescent radiation transmission means 86.

[0094] Experimental testing was performed using one preferred embodimentof the present invention with the results shown below.

[0095] Experiment 1

[0096] Six (6) oil samples were supplied ranging in opacity from Opacity1, the clearest sample, to Opacity 6, the most opaque. The emissionspectra of the six oil samples were measured using a PTI-500 fluorimeterin order to determine background emission levels. FIGS. 1 and 2 show theemission spectra of the 6 oil samples. FIG. 12 shows the full spectralrange from 380 nm to 800 nm. FIG. 13 is the same spectra but focused ona more narrow spectral range of 600 nm-700 nm where the minimumbackground fluorescence was observed. Note the strong emission in theportion of the spectrum by the oil samples (wavelengths less than 560nm).

[0097] Based on FIG. 13, it can be seen that the background emission ofall the samples is lowest in the 620-680 nanometer range. In thisembodiment a fluorescent trace material of CdSe/ZnS core/shellnanocrystals having hydrophobic surfactant layers, a peak emissionwavelength of 626 nm, and a Full Width Half Maximum (FWHM) of 24.5 nmwere chosen for the dilution and solubility experiments.

[0098] Experiment 2

[0099] Prior to dispersing the fluorescent trace materials in theOpacity 6 oil sample, 8.4 mg of fluorescent trace materials wereseparated from the toluene storage solvent through precipitation.Precipitation was achieved by adding methanol and centrifuging at 4000×Gfor 2 minutes. The supernatant was decanted 1 ml of the Opacity 6 oilsample (the most opaque oil sample) was added directly to thefluorescent trace materials pellet. The mixture was then sonicated forseveral seconds where the fluorescent trace materials were observed toquickly solvated into the oil matrix. The resulting oil/fluorescenttrace materials solution was exposed to Ultraviolet illumination and ared glow, indicative of the fluorescent trace materials emission, wasobserved. The solution was then centrifuged again at 14000×G for 4minutes. After centrifugation a large pellet of insoluble material wasnoted at the bottom of the centrifuge tube. Initially, it was believedthat the fluorescent trace materials precipitated out of solution.However, under UV excitation the supernatant still exhibited the redglow indicating the presence of the nanocrystals, while the pellet had afaint blue glow, indicative of the oil.

[0100] Experiment 3

[0101] A control experiment was conducted on the Opacity 6 oil samplewithout fluorescent trace materials. The Opacity 6 oil sample wascentrifuged at 14000×G for 4 minutes after which a large pellet wasobserved at the bottom of the centrifuge tube. An Ultraviolet light wasused to illuminate the centrifuged ample and a faint blue glow wasobserved from the precipitated pellet.

[0102] Experiment 4

[0103] A further control experiment was conducted whereby thenanocrystals were added to the Opacity 1 oil sample (the clearest oil)in the same manner as Experiment 2. The resulting optically clearoil/nanocrystal solution was observed to have a red glow indicative ofthe nanocrystals under UV illumination. The sample was then centrifugedat 14,000×G. After centrifugation a precipitated pellet was not observedalthough the red glow of the nanocrystals was clearly seen in the oilsolution under UV illumination.

[0104] Based on these results it can be concluded that the fluorescenttrace material used in this embodiment is directly soluble in the oilitself and remains in solution even under extremely high centrifugalforce. It was further concluded that the precipitate observed from thecentrifugation from the most opaque oil sample was due to insolubleparticles in the oil and not due to the fluorescent trace materialsprecipitating.

[0105] Experiment 5

[0106] To determine the minimal detectable concentration the emittingfluorescent trace materials were added to the highest opacity oil asdescribed in Experiment 2. Successive dilutions of 8.4, 4.2, 2.8, 2.1,1.4, 1.05, 0.84, 0.7, 0.6 mg/ml were made by adding more oil to theoriginal oil/fluorescent trace material 1 concentration. Thefluorescence of the oil/fluorescent trace material dilution series wasmeasured with an Ocean Optics USB 2000 spectrometer with a fiber opticdip probe attachment. The dip probe is coupled to the Ocean OpticsLS-450 light source with a 380 nm LED excitation source and the USB-2000spectrometer as the detector platform via bifurcated optical fiber.Excitation light derived from the 380 nm LED propagates down the fiberto the oil/fluorescent trace material sample and the resultantfluorescent emission is directed back up the fiber to the spectrometer.

[0107] The dilution series samples were measured by directly insertingan Ocean optics dip probe (T300) into the oil/fluorescent trace materialsolution. The dip probe was rinsed thoroughly between each measurementin order to minimize measurement error due to residual fluorescent tracematerials adhering to the probe tip. Prior to measuring the fluorescenttrace material doped samples, an oil background was run to minimizenoise from the oil emission. FIG. 14 shows the emission spectra for theOpacity 6 oil/fluorescent trace material dilution samples. FIG. 15 isthe same spectra that are focused in on the samples with the leastfluorescent trace materials dispersed in the oil.

[0108] Based on emission data above it can be determined that thedetectable concentration of fluorescent trace materials in the mostopaque oil is >1 mg/ml (>4.4 nmol/ml). In FIG. 16 the adjusted maximumemission intensity at the fluorescent trace material peak wavelength isgraphed as a function of fluorescent trace material concentration in theOpacity 6 oil sample. The adjusted maximum emission was taken to be thefluorescent emission at 626 nm minus the background signal (taken as anaverage between 480 and 570 nm).

[0109] The emission of 6 oil samples with varying opacity was measured.From these results it was noted that the minimum fluorescent lightemission from the all oil samples occurs between 620-680 nm. Fluorescenttrace materials with a fluorescent light emission peak at 626 nm (withinthe background light emission minima) were successfully solvated intohigh and low opacity oil samples and observed to glow a characteristicred. The fluorescent trace materials remained in solution even underhigh centrifugal forces indicating that the fluorescent trace materialswill not precipitate out of the oils over long periods of time when usedin power equipment. The fluorescent light emissions of varyingconcentrations of fluorescent trace materials solvated in the Opacity 6oil samples (the highest opacity oils) were measured by a fiber opticdip probe coupled to a 380 nm illumination source and a spectrometer.Fluorescence of the fluorescent trace materials in the high opacity oilwas measurable to a concentration of 1 mg/ml (4.4 nmol/ml). Clearer oilsamples with less contamination would require less fluorescent tracematerials in solution for fluorescence detection.

[0110] Having thus described the present invention by reference tocertain of its preferred embodiments, it is noted that the embodimentsdisclosed are illustrative rather than limiting in nature and that awide range of variations, modifications, changes, and substitutions arecontemplated in the foregoing disclosure and, in some instances, somefeatures of the present invention may be employed without acorresponding use of the other features. Many such variations andmodifications may be considered obvious and desirable by those skilledin the art based upon a review of the foregoing description of preferredembodiments. Many other forms of switches and other electrical contactsare known in the art and could be used in conjunction with features ofthe invention. Accordingly, it is appropriate that the appended claimsbe construed broadly and in a manner consistent with the scope of theinvention.

What is claimed is:
 1. An electrical contact, comprising: a fluorescenttrace material, wherein at least a portion of the fluorescent tracematerial is released from the electrical contact as the contactexperiences wear.
 2. The electrical contact of claim 1, wherein thefluorescent trace material comprises a nanocrystal quantum dot material.3. The electrical contact of claim 1, wherein the nanocrystal quantumdot material comprises CdSe/ZnS.
 4. The electrical contact of claim 1,wherein the fluorescent trace material is dispersed within at least aportion of the electrical contact experiencing wear.
 5. The electricalcontact of claim 1, wherein the fluorescent trace material is containedin one or more portions of the electrical contact assembly experiencingwear.
 6. The electrical contact of claim 5 wherein the fluorescent tracematerial is contained in one or more cavities formed by or securedwithin the electrical contact.
 7. An electrical contact, comprising: acavity defined in or on the contact assembly; and a fluorescent tracematerial within the cavity.
 8. The electrical contact of claim 6,wherein the cavity is configured so that the fluorescent trace materialis released from the cavity into a surrounding medium when the contactassembly has eroded to a detectable erosion point.
 9. The electricalcontact of claim 6, wherein the cavity is configured so that thefluorescent trace material is released from the cavity into asurrounding medium when the contact assembly has eroded sufficientlythat an opening develops to the cavity.
 10. The electrical contact ofclaim 6, wherein the fluorescent trace material is a nanocrystal quantumdot material.
 11. A contact assembly, comprising: a conductive base; acontact tip connected to the base or contact fabricated entirely oftungsten-based material; and a cavity defined in the sacrificialcontact, wherein the cavity contains a fluorescent trace material. 12.The contact or contact assembly of claim 10, wherein the cavity isconfigured so that the fluorescent trace material is released from thecavity into a surrounding medium when the contact or contact tip haseroded to a detectable erosion point.
 13. The contact or contactassembly of claim 10, wherein the fluorescent trace material consists ofthe elements chosen from the elements of periodic groups 11-VI, III-V orIV-VI and are nanocrystals ranging in size from 2 to 10 nanometers. 14.A device for detecting fluorescent trace material in a mediumsurrounding a contact assembly, comprising: a source of electromagneticradiation; a detector for sensing the level of fluorescent radiationgenerated by the fluorescent trace material in response to theelectromagnetic radiation source; a means for transmittingelectromagnetic radiation from the electromagnetic radiation source tothe surrounding medium; and a means for transmitting fluorescentradiation between the surrounding medium and the detector.
 15. Thedetection device of claim 14, wherein the means for directingelectromagnetic radiation from the electromagnetic radiation source tothe surrounding medium and the means for transmitting fluorescentradiation between the surrounding medium and the detector comprise atleast one optically-transmissive conduit.
 16. The detection device ofclaim 15, further comprising a connector on the at least oneoptically-transmissive conduit configured to engage an access port in toan enclosure of the electrical contact assembly.
 17. The detectiondevice of claim 14, wherein the electromagnetic radiation source is anultraviolet light emitting source.
 18. The detection device of claim 14,wherein the electromagnetic radiation source emits electromagneticradiation with a broad-band wave-length.
 19. A device for detectingfluorescent trace material in a medium surrounding a contact assembly,comprising: a source of electromagnetic radiation; a detector forsensing the level of fluorescent radiation generated by the fluorescenttrace material in response to the electromagnetic radiation source; afirst optical guide component for directing electromagnetic radiationfrom the electromagnetic radiation source to at least a portion of thesurrounding medium; and a second optical guide component for directingfluorescent radiation from the fluorescent trace material in thesurrounding medium the detector.
 20. The detection device of claim 19,wherein the electromagnetic radiation source is an ultraviolet lightemitting source.
 21. The detection device of claim 19, wherein theelectromagnetic radiation source emits broad-band electromagneticradiation with a wave-length of about 254 nm.
 22. A method fordetermining erosion of a contact assembly, the method comprising:providing a fluorescent trace material within the contact assembly;allowing the contact assembly to be eroded until at least a portion ofthe fluorescent trace material is released into a surrounding medium;and monitoring at least one point in the surrounding medium to detect aquantity of fluorescent trace material dispersed into the surroundingmedium as an indicator of erosion of the contact assembly.
 23. Themethod of claim 22, wherein the fluorescent trace material is providedwithin a cavity defined in the contact assembly.
 24. The method of claim22, wherein the monitoring step further comprises the steps of:directing electromagnetic radiation into the surrounding medium; andsensing the amount of radiation emitted by the fluorescent tracematerial to determine the amount of fluorescent trace material in thesurrounding medium.
 25. The method of claim 24, wherein theelectromagnetic radiation is ultraviolet radiation.
 26. The method ofclaim 24, wherein the electromagnetic radiation has a wave-length ofabout 254 nm.
 27. The method of claim 24, wherein the ultravioletradiation is generated from a source located within an enclosuresurrounding the electrical contact assembly.
 28. The method of claim 27,wherein the ultraviolet radiation is generated from a source located ina fluorescent trace material detecting device.
 29. The method of claim22, wherein the step of monitoring the surrounding medium comprises thesteps of: circulating the surrounding medium through a particulateconcentration device; directing electromagnetic radiation onto thefluorescent trace material in the particulate concentration device; anddetecting the level of fluorescent radiation emitted in response to theelectromagnetic radiation.
 30. The method of claim 29, wherein: theparticulate concentration device comprises a transparent or translucentobservation wall; and the electromagnetic radiation is directed throughthe observation wall to the fluorescent trace material.
 31. A method fordetermining the presence of fluorescent material associated with wear ofan electrical contact assembly, comprising the steps of: generatingelectromagnetic radiation; directing the electromagnetic radiation tofluorescent material indicating wear of the contact assembly; detectingthe amount of fluorescent radiation generated by the fluorescentmaterial in response to the electromagnetic radiation; and determining alevel of wear of the electrical contact assembly form the amount offluorescent radiation detected.
 32. A method for determining the levelof a fluorescent trace material present in a medium surrounding anelectrical contact assembly, comprising the steps of: circulating thesurrounding medium through a particulate concentration device containinga collection surface; directing electromagnetic radiation to theparticulate concentration device; and detecting the amount offluorescent radiation generated by the fluorescent trace materialcollected by the particulate concentration device in response to theelectromagnetic radiation.